Apparatus for the production of polymers by irradiation



United States Patent 3,472,752 APPARATUS FOR THE PRODUCTION OF POLYMERSBY IRRADIATION John B. Gardner, Lake Jackson, Tex., Charles F. Smith,Tulsa, Okla., and Billy G. Harper, Lake Jackson, Tex., assignors to TheDow Chemical Company, Midland, Mich., a corporation of Delaware Originalapplication Feb. 25, 1965, Ser. No. 435,299, now Patent No. 3,414,499.Divided and this application Nov. 13, 1967, Ser. No. 704,199

Int. Cl. B01k 1/00; C07c 3/24 US. Cl. 204-193 1 Claim ABSTRACT OF THEDISCLOSURE This is a division of application Ser. No. 435,299, filedFeb. 25, 1965, now Patent No. 3,414,499.

This invention relates to an apparatus and process for the irradiationpolymerization of unsaturated compounds and more particularly relates toan apparatus and process whereby polymers of different average molecularweight may be simultaneously yet separately produced by the action ofionizing radiation.

The polymerization of unsaturated compounds by ionizing radiation iswell known. It is likewise well known that the mechanism ofpolymerization involves the formation of free radicals on theunsaturated compound by application of high energy particles theretowith a subsequent joining of the molecules to form more or less linearpolymers. Average molecular weight is a function of intensity so it isimportant that the intensity of the radiation reaching the monomer becontrolled. High intensity produces loW molecular weight polymer and lowintensity produces high molecular weight polymers. If irradiation iscontinued after an apprecibale amount of polymer has been formed, oftenadditional free radical sites will form on the polymer chain andcross-linked and branched-chain polymers are produced. According to themethods now known and employed, therefore, the polymers produced byradiation techniques usually require a number of different reactors toproduce polymer species having various molecular weights and degrees ofcrosslinking. These procedures do not efiiciently use the availableradiation but rather utilize only a narrow intensity range in any givenreactor.

It is highly desirable for purposes of end use and fabrication thatpolymers having different average molecular weights be available. Inorder to supply this need, the typical radiation-produced polymer isfractionated into different molecular weight fractions. However, thefractionation is not only a time consuming and expensive operation butoften tends to degrade the polymer and otherwise alter the group ofpolymer species being separated.

It is an object of this invention, therefore, to provide an apparatusand a process whereby polymerizable unsaturated monomeric materials canbe polymerized by the action of ionizing radiation to produce polymershaving different average molecular weights. It is a further object3,472,752 Patented Oct. 14, 1969 ice of this invention to provide anapparatus and process for simultaneously producing two or more polymerseach having different average molecular weights.

A further object of this invention is to effectively utilize allradiation of both high and low intensity.

Other objects and advantages of the process will become apparent from areading of the following portions of the specification and claim.

It has now been discovered that polymers having different averagemolecular weights may be produced by providing a. source of ionizingradiation axially located at the center of two or more concentric pipes,and passing one or more unsaturated monomers through the annular spacesprovided by the concentric pipes. The resulting polymeric product orproducts may then be separately collected and utilized without thenecessity of fractionation.

The accompanying drawing illustrates the invention embodied in apreferred form, it being understood that the form of the invention issusceptible of modification without departure from the true spirit andscope thereof.

FIGURE 1 is a side elevation, largely in section, of the reactor showinga scheme of delivery thereto of multiple streams of unsaturated monomerfrom a single source.

FIGURE 2 is a sectional plan view of the reactor at section 2-2.

Referring to the drawings (in which like numbers are used to denote likeparts) there is shown, in FIGURE 1, a reactor 10 composed of a centraltube or core 11 which contains a C0 rod 12 as the radiation source. Thiscentral tube or core 11 is surrounded by concentric reactor tubes ofever increasing diameter. The first such concentric reactor tube 13 isclosest to the radiation source, reactor tube 14 is more distant andreactor tube 15 is the most distant from the irradiation source.Unsaturated monomer storage tank 22 is shown connected to individualpumps 23, 24, and 25 which supply the annular spaces 26, 27, and 28through lines 16, 17 and 18. In the upper portion of reactor 10 areproduct outlet lines 19, 20 and 21. It is to be understood that ifdifferent monomers are used, a different storage tank would normallysupply each of the individual pumps.

FIGURE 2 is a plan section taken at plane 22 through FIGURE 1 and showsthe core 11 with a C0 rod 12 in the central portion thereof.concentrically around this central core 11 are placed product tubes 13,14 and 15 forming annular reaction spaces 26, 27 and 28, respectively.

According to the process of this invention, polymerizable unsaturatedorganic monomer such as vinyl chloride is fed to one or more of theannuli of the reactor. Several streams of the same monomer may be fed tothe different annuli to produce polymers of various molecular weights,or several different monomers may be fed each to its own annulus toproduce several types of polymers simultaneously. As is well known, theradiation intensity will vary with distance from the source so virtuallyany molecular weight of polymer may be obtained by supplying the propermonomer to the portion of the reactor which is the necessary distancefrom the radiation source. It is likewise well known that high intensityradiation produces low molecular weight polymers whereas low intensityradiation produces high molecular weight polymers. As is shown by FIGURE1 of the drawing, vinyl chloride may be fed to three different annuli ofthe reactor to produce three different polymer species. That monomer fedto the annulus closest to the radiation source produces a relatively lowmolecular weight product whereas the most distant annulus produces arelatively high molecular weight product. In this process, however, noproduct separation is necessary since all monomer streams are alreadyseparate and the polymer from each stream may simply be removed fromunreacted monomer and utilized without the usual processing.

While the reactor may be constructed of any suitable non-reactive,material unaffected by radiation, experience has shown stainless steeland titanium to be particularly suitable. While wall thickness of theindividual concentric tubes is not critical, this is determined byoptimizing strength and permeability factors for each reactor. The wallsmust be sufliciently heavy to be structurally strong but sufficientlythin so as to not absorb too much radiation, particularly if a largenumber of concentric tubes are to be employed. In general, the innertube or two may be thinner than the outer tubes. An inner tube thicknessof from about 1 mm. to about mm. and an outer tube thickness of from 1.5or 2.0 to mm. is generally useful for stainless steel. If titanium isemployed, the wall thickness need be only /3 to /2 this amount.

The size of the annular spaces between the concentric pipes or tubes maybe varied depending on the desired results. More closely spaced tubesleaving very thin annular spaces will produce polymer having a morenarrow molecular weight spread than will the more widely spaced tubes.

Total dose is easily controlled in this process by simply increasing ordecreasing the residence time of the unsaturated monomer and polymerwithin the reactor. Residence time may also be easily controlled over awide range by changing the flow rate of the monomer or by changing theannular distance or both. The total dose necessary to form polymer of agiven type will vary depending on the monomer, but these values areavailable in the published literature and are well known to thoseknowledgeable in this field.

Monomeric unsaturated compounds may be fed into either the top or bottomof the reactor, may be in either liquid, gaseous or even solid form andmay be present in bulk or as solutions or emulsions in relatively inertsolvents or carriers. Likewise, the process may be easily used either asa batch or continuous process.

Any monomeric unsaturated compound which will polymerize in the presenceof ionizing radiation may be employed in the process of this inventionbut the vinyl compounds are particularly useful. Typical monomersinclude vinyl chloride, ethyl acrylate, methyl methacrylate, ethylene,acrylic acid, allyl chloride, allyl alcohol, 'vinyl morpholinone,acrylamide. Copolymers, terpolymers, polysulfones, etc. may also beprepared by passing mixtures of monomers through the reactor. Any of thewellknown mixtures of liquid polymerizable vinylidene compoundsheretofore used for the production of copolymers can be employed inproducing copolymers by the method of the present invention.

Any ionizing radiation source may be used in this process so long as itis capable of free radical production in unsaturated compounds and isphysically capable of emitting high energy particles radially from acentral source. A material which can be formed into a rod isparticularly desirable but even a point source of radiation is usefulherein. Materials such as radium, Cs Sr La Co In I Ba Pb and Bi may beused.

EXAMPLE 1 A reactor as shown in FIGURE 1 was used in continuously andsimultaneously produce vinyl chloride polymers having three differenteverage molecular weights. The hollow core had a radius of 10 cm. and awall thickness .4 of 7 mm., while the outer concentric tubes were eachof a wall thickness of 10 mm. and had radii of 50 cm., cm. and cm.,respectively. The reactor was 700 cm. long and was operated at ambientconditions of temperature and pressure. Monomeric vinyl chloride was fedto each of the annuli at the rate shown. In the following table, resultsof this experiment are given together with the intensity of theradiation to which the vinyl chloride was subjected.

Radius, cm 50 J0 13 Volume of annulus, cc 5. 3X10 12. 3X10 1t). 2X10Weight of vinyl chloride fed, lbs/hr- 60, 000 28,000 0, 000 Av.Intensity m.r.lhr 1. 2 0.125 0. 013 55 10 2 5, 500 2, 360 725 14, 000150, 000 850, 000

EXAMPLE 2 Following the same general procedure of Example 1 and usingthe same equipment, polymethylmethacrylate polymers were prepared whichhad three different average molecular weights. In order to produce agreater variation in dose rate between the various annular spaces,additional shield tubes composed of about 3 mm. stainless steel wereinserted. Fifty grams of distilled methylmethacrylate were purged'withnitrogen, divided into three different equal portions and one portionwas placed in each of the reactor annular spaces. Each portion of themonomer was irradiated by the Co source until it had received a totaldose of 0.25 megarad. At this time, the polymer was removed from thereactor, dissolved in acetone, precipitated with methyl alcohol anddried in an oven. A weighed sample of the dried material incyclohexanone was then used to determine the intrinsic viscosity of thepolymer which is a function of the polymers molecular weight. Thefollowing table summarizes the results obtained.

In a like manner, other radiation polymerizable materials such asacrylic acid, acrylamides, acrylic esters, vinyl-vinylidene copolymersand vinyl carboxylates may be likewise polymerized in masspolymerizations as illustrated above or as suspensions, solutions oremulsions.

We claim:

1. A reactor for the simultaneous polymerization of polymerizableunsaturated monomeric materials which comprises a central tubular core,a high energy radiation source contained within said core, a pluralityof concentric tubular reactor shells outward from said central tubularcore which form a plurality of reaction annuli outward from said centraltubular core, means for introducing a polymerizable unsaturatedmonomeric material into each such reaction annulus and separate meansfor removing the polymerized product therefrom.

HOWARD S. WILLIAMS, Primary Examiner

